Most semiconductor and related products, such as transistors, diodes, light-emitting diodes, microelectronic machine systems or micro-electro-mechanical systems (MEMS), planar waveguide structures, integrated circuits, and other microdevices, are manufactured contemporaneously in large batches on a large wafer. These wafers are typically composed of Si, GaAs, GaP, InP, Ge, silicon carbide, silicon nitride, sapphire, polymers, or other materials. The manufacture of these products or devices is most often performed using conventional fabrication techniques, such as, but not limited to, photolithography, oxidation, implantation, deposition, etching, epitaxial growth, and/or spin coating. Upon complete manufacture of these device-laden wafers, the individual devices must be separated or “singulated”—a process that is typically referred to as “dicing.” In many singulation processes, the wafers are first separated into rows of components—a process typically referred to as “slicing”—but “slicing” and “dicing” may be used interchangeably. The individual devices are referred to as “die” or “dice.” The areas on a wafer between active parts of adjacent dice are referred to as the “streets” or “dice lanes.” The streets are limited to a minimum width because of the wafer material that is removed or destroyed during the dicing process. The wafer area that is completely removed by the dicing process is called a “kerf,” and the rest of the street must accommodate any damage zone around the kerf and any manufacturing misalignment or dicing deviation from the straightness of the kerf.
Conventionally, dicing is performed using a wafer saw or by a technique called “scribe and break,” in which a wafer is notched with a scribe line, often by a diamond point, and is then cleaved along the scribe line. Due to low-yield issues, such as unpredictable propagation of microcracks as well as observable damage to devices, associated with scribe-and-break techniques, mechanical dicing saws have become the predominant tool for dicing wafers. Conventional slicing blades typically have a dimension of about 50 to 200 microns (μm) along the cutting axis and produce cuts that are wider than the blades. The blades are that wide in order to withstand the stresses of repeatedly making straight cuts through the hard, thick materials of conventional wafers. The wide cuts made by the mechanical cutting blades often significantly reduce the number of rows and columns of die that can be fit onto each wafer. Dicing blades also tend to wear relatively quickly, such that the width of their cuts may vary over time. In some cases, the blades can be inadvertently bent, and then they produce curved or slanted cuts or increased chipping.
In addition, the dicing process creates small chips as it creates sharp edges and sharp corners along singulation paths and thereby makes the devices more susceptible to damage, particularly from external bumps. Dicing saws also tend to create microcracks that extend into the layers of devices from the kerf, reducing yields. In addition, microcracking may not be evident when the devices are tested, but may later propagate into the layers to later cause device failure, which reduces the reliability of the devices and the equipment based on them. Although some microcracking may be avoided by slowing the mechanical sawing speed, microcracking is very difficult, if not impossible, to avoid in some materials. Dicing saws also typically require the use of water as a lubricant and/or coolant, and the water can create problems or lower yields for certain types of materials or devices, such as MEMS.
Laser cutting is becoming an attractive alternative to the conventional mechanical cutting techniques. One reason for using laser dicing is that lasers can cut curved die such as arrayed waveguide gratings from a wafer, unlike either of the two conventional techniques. In addition, lasers can often cut without the use of water, which is of great importance for the manufacture of devices that are water-sensitive, such as MEMS. Lasers also offer the potential of the smallest street width available, due to a potentially very small kerf width and the possibility of very accurate alignment of the laser in relation to the workpiece (wafer).
Lasers also offer the ability to form patterns on wafers, creating features such as trenches or notches that can be made by scanning the laser across the surface and cutting only the film or cutting partly through the wafer, as opposed to mechanical-saw dicing techniques that permit only through-cuts. The partial cutting techniques can be used to make features on die or to perform laser scribing for a scribe-and-break process, for example.
Lasers also offer great potential for the drilling of vias through or into the film or substrate material. Such via drilling is of interest for reasons that may include, but are not limited to, allowing a ground to be contacted through the backside of a die, allowing die to be stacked on top of each other inside one package (“three-dimensional packaging”), or allowing devices to be mounted in a “flip-chip” BGA fashion such that the active devices would be facing up (with implications for MEMS or front-side cooling of integrated circuits or laser diodes). The diameter of these vias can range from several microns up to several hundred microns, and the die thicknesses of interest vary from tens of microns to almost 1,000 μm. Few production-worthy solutions currently exist for the drilling of such high-aspect-ratio vias, and those such as plasma etching tend to be cumbersome and expensive for equipment and maintenance.
Better methods for processing wafers and the materials they support are, therefore, desirable.